(1) Field of the Invention
This invention relates to a liquid crystal display device, and more specifically, to an improvement of electrodes for displaying a multi-tone image.
(2) Description of the Related Art
Ferroelectric liquid crystals have a very short reorientation response time in comparison with twisted-nematic type liquid crystal which is widely used in display devices, and have been reported by Noel A. Clark and Sven T. Lagerwall in "Applied Physics Letters" vol. 36 No. 11 (June 1, 1980), pp. 899 to 901. The ferroelectric liquid crystals have another advantage of a memory function that an optical state changed by an application of electric field is remained after a removal of the electric field. A viewing angle of a display using the ferroelectric liquid crystal is wide.
Those features of ferroelectric liquid crystals allow an achievement of manufacturing a liquid crystal display which keeps a high image quality with increased number of pixels. An image having a high contrast, a high definition and a wide area is easily obtained without using thin-film transistor switches which are used in active-matrix type display devices.
The ferroelectric liquid crystal, however, has a drawback that a multi-tone image cannot be displayed by controlling magnitude of electric field applied to the ferroelectric liquid crystal. Unless such drawback is improved, the ferroelectric liquid crystal cannot be used for TV display. The application of ferroelectric liquid crystal to a plane display is proposed in U.S. Pat. No. 4,367,924, but the displayed image has only black or white.